Apparatus for using cast-off heat to warm water from household water heater

ABSTRACT

A retrofit heat transfer unit, including: a housing for the retrofit unit, including inlet and outlet ports for water and refrigerant; a water pump, in fluid communication with the water inlet port, the water pump adapted to pump water from a water source; a heat exchanger, in fluid communication with the water pump, the water outlet port, the refrigerant inlet port and the refrigerant outlet port; and a thermostat, configured to measure a temperature of the pumped water and activate the water pump when the water is below a predefined low temperature and cease to pump when water is above a predefined high temperature. The retrofit unit is also adapted to receive heated refrigerant fluid from an air conditioner and direct the refrigerant through the heat exchanger and direct the pumped water into the heat exchanger so that the refrigerant heats the water and the water cools the refrigerant.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a heat transfer apparatus and, moreparticularly, to an apparatus for transferring heat from an airconditioner unit to water from a water heater.

A legacy air conditioner uses refrigerant to cool down a space. Therefrigerant (e.g. Freon) cools to very low temperatures which is usefulin cooling an indoor space. A fan blows air over Evaporator coils (coilswhich contain cool refrigerant) to cool the room. Another characteristicof the refrigerant used in air conditioners is that it absorbs heat fromthe air in the room and returns cooled air. The absorbed heat must bereleased though, and this is the job of the Condenser. Condenser coilsare usually located outdoors and have a fan which blows air over thecoils (which contain very hot refrigerant, often between 70° C. and 80°C.). The fan air cools the coils and refrigerant so that the refrigerantcan be reused to cool the indoor space. In some systems water is used tocool the hot coils instead of fan-blown air.

Various attempts have been made to utilize the heat generated by the airconditioning system to heat water. Specifically, a number of patentspertain to the use of the heat to warm pool water. U.S. patentapplication Ser. No. 12/706,883 teaches an air conditioner and poolheater dual system, functioning as a combination air conditioner andwater heater having a heat exchanger that includes arefrigerant-to-water heat exchanger, a gas compressor, and at least oneevaporator coil. The dual system is capable of heating a pool andrefrigerating a house simultaneously using only one compressor. The '833application fails to disclose a domestic water heater-air conditionerarrangement. A pool heater already includes a pump (for filtering thewater) and air conditioning unit (for warming the water), therefore itis logical to expel the cooled air into an enclosed space. A waterheater, on the other hand, does not have an existing pump or heatingsystem that has a byproduct which creates cool air. It would thereforebe novel to provide a retrofit heat transfer apparatus disposed betweenan air conditioner and a water heater.

U.S. Pat. No. 5,560,216 also teaches a combination air conditioner andpool heater. All of the aforementioned deficiencies apply equally here.

U.S. Pat. No. 4,194,368 teach a combination split system air conditionerand compression cycle domestic hot water heating apparatus including aconventional split system air conditioner combined with a compressioncycle or heat pump system for supplying heat to a domestic water heater.The '368 system is a ready made system where both the air conditionerand heating tank have been specially designed. The system does not teacha retrofit system which can be added to existing air conditioning andwater heating systems.

It would be highly advantageous to have a system that utilizes thegenerated/cast-off heat of an air conditioner to warm water, especiallyin domestic water-heater systems. It would be most advantageous toprovide a retrofit unit that can be simply installed in existing setupswhich have standard air conditioning and water heating systems, withoutremodeling either the air conditioner or the water heater. Such anapparatus would be especially useful in high-rise buildings which (forboth logistical and esthetic reasons, enforced by local buildingordinances) cannot take advantage of solar heating systems and thereforehave to both cool the living areas and heat water during the hotseasons.

SUMMARY OF THE INVENTION

The innovative retrofit heat transfer system of the immediate innovationuses heat produced by an air conditioner compressor to heat the water ina (household) water heater. When refrigerant gas is compressed back intoa liquid the line holding the liquid gets very hot (75° C.-85° C.). Thisheat must be released for the liquid to cool. The refrigerant runsthrough a coaxial coil heat-exchanger or a plate heat-exchanger in orderto cool the refrigerant liquid, which then continues to travel throughthe condensation coils for continued working. When the air conditioneris active then refrigerant liquid flows through the heat exchanger whilecool water is pumped from the water heater—by a water pump—through theheat exchanger, thereby bringing the cool water into contact with thehot refrigerant fluid line. The hot fluid line can have an averagetemperature of 80° C. The pump action draws cool or cold water from thewater heater tank and runs the water through the heat exchanger wherethe refrigerant is flowing at a temperature of about 80° C., therebywarming the water in the tank after a few cycles through the heatexchanger. At the same time, the refrigerant liquid is cooled by thewater from the water tank, removing the need for activating the coolingfan. Therefore innovative unit lowers the cost of running the airconditioner (the cooling fan only runs when the water in the heatingtank is too warm to cool the refrigerant fluid) as well as lowering thecost of heating water (the water only needs to be heated for a veryshort period before becoming hot enough for domestic use). The retrofitunit causes the air conditioner to heat water—at no additional cost ofenergy—while at the same time cooling the house at a potentially lowercost than normal.

According to the present invention there is provided a retrofit heattransfer unit, including: (a) a housing for the retrofit unit,including: a water inlet port, a water outlet port, a refrigerant inletport and a refrigerant outlet port; (b) a water pump, in fluidcommunication with the water inlet port, the water pump adapted to pumpwater from a water source; (c) a heat exchanger, in fluid communicationwith the water pump, the water outlet port, the refrigerant inlet portand the refrigerant outlet port; and (d) a thermostat, configured tomeasure a temperature of the pumped water, pumped from the water source,such that the water pump is configured to pump water from the watersource when the pumped water is below a predefined low temperature andcease to pump the water when the pumped water is above a predefined hightemperature, and where the retrofit unit is adapted to receive heatedrefrigerant fluid from an air conditioner at the refrigerant inlet portand direct the received heated refrigerant fluid through the heatexchanger and further adapted to direct the pumped water into the heatexchanger such that heat from the heated refrigerant fluid istransferred to the water, pumped into the heat exchanger, cooling theheated refrigerant fluid and heating the water, the heated water exitingthe housing via the water outlet port.

According to further features in preferred embodiments of the inventiondescribed below the heat exchanger is a co-axial coil heat exchanger ora plate heat exchanger.

According to still further features in the described preferredembodiments the source is a domestic water heater.

According to still further features the air conditioner has a coolingfunction and a heating function for electively cooling and heating anindoor space.

According to still further features the retrofit unit is configured toreceive the heated refrigerant via the refrigerant inlet port from theair conditioner when the air conditioner is in a cooling state orheating state.

According to still further features a differential between thepredefined low temperature and the predefined high temperature is in arange between about 5° C. and 20° C.

According to still further features the water source is a water supplyline from an outdoor water provider and wherein the unit furtherincludes: (e) a valve configured to admit water from the supply linewhen heated water is being drawn from a water heater to a domestic waterdistribution system, wherein the water heater is operationally coupledto the retrofit unit via the water inlet port and the water outlet port.

According to still further features the unit further includes a switchfor electively activating and deactivating the thermostat.

According to still further features the unit further includes (e) apressostat, configured to deactivate an outdoor cooling fan of the airconditioner when pressure in outdoor coils of the air conditioner isbelow a predefined compression pressure. Further including a means forcircumventing the pressostat.

According to the present invention there is provided a method ofincreasing the combined efficiency of an air conditioner and a waterheater tank, including the steps of: (a) interposing a retrofit heatexchange unit between an outdoor unit of the air conditioner and thewater heater tank; (b) cutting a refrigerant line between a compressorand a 3-way valve of the air conditioner; (c) coupling the refrigerantline from the compressor to a refrigerant inlet port located on ahousing of the retrofit unit; (d) coupling the refrigerant line the3-way valve to a refrigerant outlet port located on the housing; (e)coupling the water heater tank to a water inlet port located on thehousing, such that a water pump, disposed inside the housing and coupledto the water inlet port, when activated, is configured to draw waterfrom the water heater tank; and

(f) coupling the water heater tank to a water outlet port located on thehousing, such that heated water, when exiting a heat exchanger disposedin the housing and operationally coupled to the water outlet port, exitsthe water outlet port and enters the water heating tank, so thatrefrigerant from the air conditioner heats the water from the waterheater tank, in the heat exchanger.

According to still further features the method further includes the stepof (g) connecting a pressostat, disposed in the housing, to the airconditioner, for disconnecting a cooling fan of the outdoor unit whenpressure in coils of the outdoor unit falls below a predeterminedcompression pressure.

According to still further features the method further includes the stepof: (h) installing in a control panel, operationally associated with thehousing or the retrofit unit, a circumvention mechanism forcircumventing the pressostat.

According to still further features the method further includes the stepof: (g) installing in a control panel operationally associated with thehousing, a switch, for electively activating and deactivating the waterpump.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is a typical vapor compression refrigeration system known in theart;

FIG. 2 is a schematic diagram of the invention within a general setup,with the air conditioner in a cooling state;

FIG. 3 is a schematic diagram of the invention within a general setup,with the air conditioner in a heating state;

FIG. 4 is a schematic diagram of a second embodiment of the invention,with the air conditioner in a heating state;

FIG. 5 is a schematic illustration of a prior art water heating systemand an air conditioner prior to installation of the retrofit unit of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The principles and operation of a retrofit heat transfer systemaccording to the present invention may be better understood withreference to the drawings and the accompanying description.

Referring now to the drawings, FIG. 1 is a typical vapor compressionrefrigeration system known in the art. The vapor-compression uses acirculating liquid refrigerant as the medium which absorbs and removesheat from the space to be cooled and subsequently rejects that heatelsewhere. FIG. 1 depicts a typical, single-stage vapor-compressionsystem. All such systems have the following four components: acompressor 12, a condenser 14, a Thermal expansion valve 16, and anevaporator 18. Circulating refrigerant enters compressor 12 in thethermodynamic state known as a saturated vapor (i.e. gaseous state) andis compressed to a higher pressure, resulting in a higher temperature aswell. The hot, compressed vapor is then in the thermodynamic state knownas a superheated vapor and it is at a temperature and pressure at whichit can be condensed with typically available cooling water or coolingair. That hot vapor is routed through a condenser where it is cooled andcondensed into a liquid by flowing through a coil or tubes with coolwater or cool air flowing across the coil or tubes. This is where thecirculating refrigerant rejects heat from the system and the rejectedheat is carried away by either the water or the air (whichever may bethe case).

The condensed liquid refrigerant, in the thermodynamic state known as asaturated liquid, is next routed through an expansion valve where itundergoes an abrupt reduction in pressure. That pressure reductionresults in the adiabatic flash evaporation of a part of the liquidrefrigerant. The auto-refrigeration effect of the adiabatic flashevaporation lowers the temperature of the liquid and vapor refrigerantmixture to where it is colder than the temperature of the enclosed spaceto be refrigerated.

The cold mixture is then routed through the coil or tubes in theevaporator. A fan circulates the warm air in the enclosed space acrossthe coil or tubes carrying the cold refrigerant liquid and vapormixture. That warm air evaporates the liquid part of the coldrefrigerant mixture. At the same time, the circulating air is cooled andthus lowers the temperature of the enclosed space to the desiredtemperature. The evaporator is where the circulating refrigerant absorbsand removes heat which is subsequently rejected in the condenser andtransferred elsewhere by the water or air used in the condenser.

To complete the refrigeration cycle, the refrigerant vapor from theevaporator is again a saturated vapor and is routed back into thecompressor 12.

FIG. 2 illustrates a schematic diagram of the invention within a generalsetup, where the air conditioner is in a cooling state. Unit 100 is theinventive retrofit heat transfer unit of the immediate invention. An airconditioner 150 is coupled to unit 100 in a manner that will be furtherdetailed below. A water heating system 170 is connected to the householdplumbing system in a standard fashion and to unit 100 in a manner thatwill be described in further detail below.

Air conditioner 150 includes a compressor 151, a two-way expansion valve154, an outdoor unit including coils 152 and fan 155 and an indoor unitincluding coils 153 and fan 157. Air conditioners which have anadditional heating feature also include a three-way valve 105 (sometimescalled a four-way valve when including the inlet port).

Water heater system 170 includes a water heater tank 181, an intake pipe172, a cold outlet pipe 174, a hot intake pipe 176 and a hot outlet pipe178. A thermometer 180 provides a temperature read for cold outlet pipe174 and a thermostat 179 activates unit 100 and designates the desiredtemperature of the water. A supply line faucet/valve 177 control thesupply of water from an outdoor water source to the heating tank. Hotoutlet pipe 178 is coupled to water distribution system 182 from wherethe hot water is distributed throughout the living area.

Heat transfer unit 100 includes a heat exchanger 108 and a water pump106 disposed within housing 101 of the unit. Housing 101 furtherincludes inlet and outlet ports and connecting lines/pipes forfacilitating an efficient retrofit installation of unit 100. Refrigerantinlet port 120 is adapted to receive a connection refrigerant line (hot)103 from compressor 151. Inside housing 101 coupling refrigerant line104 connects inlet port 120 to heat exchanger 108. A refrigerant outletline 107 runs from heat exchanger 108 to an outlet port 122 on housing101. A refrigerant line 109 running from outlet port 122 enters 3-wayvalve 105 and from there to either the indoor or outdoor coils dependingon which state the air conditioner is in (heating or cooling). Housing101 further includes a water inlet port 124 adapter to receive waterfrom a water source (in the depicted embodiment in FIG. 2 the watersource is a domestic water heating tank). A water line 175 runs fromport 122 to water pump 106 and from pump 106 to heat exchanger 108. Awater outlet port 126 is disposed in housing 101 and coupled to heatexchanger 108. Water outlet port 126 is adapted to be connected to awater pipe 176 which carries heated water to given destination (in thedepicted embodiment in FIG. 2 the destination is a domestic waterheating tank).

When air conditioner 150 is in a cooling state, cold refrigerant gas(saturated vapor) travels (direction of travel is indicated by thearrows above the various different gas and liquid lines/coils) throughindoor coils 153 whereupon indoor fan 157 blows ambient air over thecoils and out of the evaporator unit (usually situated in some form ofliving space such as a room, office, hall, etc.). In general, the gasabsorbs the heat in the ambient air so that cooled air is expelled,cooling (and dehumidifying) the space. The gas continues to travelthrough the gas line and enters 3-way valve 105 (which is part of airconditioning unit 150 although not drawn as such), whereupon the gas isdirected to compressor 151. At the compressor, the gas is compressed toa higher pressure, resulting in a higher temperature as well. The hot,compressed vapor is then in the thermodynamic state known as asuperheated vapor and it is at a temperature and pressure at which itcan be condensed with typically available cooling water or cooling air,thereby releasing the absorbed heat. The superheated gas/vapor runsalong a hot line 103/104 between compressor 151 and heat exchanger 108.At heat exchanger 108, the hot vapor is cooled and condensed into aliquid by flowing through (in one preferred embodiment) the coaxial coilof the heat exchanger with cool water flowing across the internal coilsuch that heat is transferred from the heated line to the water which iscirculated back into water heating tank 181 via hot inlet pipe 176. (Thecoaxial coil heat exchanger will be discussed in further detail below.)Pump 106 pumps cold or cool water from water heater tank 181—via coldoutlet line 174/175—into heat exchanger 108. Heat exchanger 108 acts asa Condenser when infused with cold water. The condensed cooled (or atleast cooler) liquid refrigerant then travels into 3-way valve 105 andfrom there into outdoor coils 152. If the liquid has been sufficientlycooled by heat exchanger 108 then outdoor fan 155 is not activated.

In one preferred embodiment, a pressostat 160 is coupled to the outdoorcoils 152 and fan 155. Pressostat 160 is configured to detect whetherthe pressure in the coils in below a predetermined level or not. If thepressure is below the predetermined level, then the refrigerant issufficiently cool and fan 155 is not needed. Otherwise, if the pressureis too high (i.e. the refrigerant is still too hot), then fan 155continues to blow air over coils 152 to cool the refrigerant (see belowfor further details).

Cooled liquid continues to flow from coils 152 to expansion valve 154where the refrigerant liquid is partially converted back into a cold gas(by undergoing an abrupt reduction in pressure), starting the cycleover.

If the water coming out of heating tank 181 rises above a predefinedtemperature, then thermostat 179 deactivates water pump 106 so that nonew cool water is pumped through heat exchanger 108. In such a case, thehot gas is not cooled by the heat exchanger and outdoor fan 155 must beactivated to cool outdoor coils 152 (which act as the Condenser) in thenormal manner. In some embodiments, a pressure switch (e.g. such as apressostat pressure switch discussed above) determines whether theoutdoor fan 155 must be activated or not. In general, the differentialbetween the predefined low temperature at which the pump is activatedand the predefined temperature at which the pump ceases is in a rangebetween about 5° C. and 20° C.

Another possible configuration is shown in FIG. 3. FIG. 3 illustrates aschematic diagram of the invention within a general setup, with the airconditioner in a heating state. In the heating state, 3-way valve 105reverses the direction in which the refrigerant flows. When heating, theair conditioner/heater uses a refrigerant as an intermediate fluid toabsorb heat where it vaporizes (outside), in the evaporator, and then torelease heat where the refrigerant condenses (inside), in the condenser.The refrigerant flows through insulated pipes between the evaporator andthe condenser, allowing for efficient thermal energy transfer atrelatively long distances.

In heating mode, outdoor coil 152 is an evaporator, while indoor coil153 is a condenser. The refrigerant flowing from the evaporator (outdoorcoil) carries the thermal energy from outside air (or ground) indoors.After traversing coils 152 the refrigerant enters 3-way valve 105 and isdirected towards compressor 151. The temperature of the fluid isaugmented by compressing the fluid at compressor 151. (The direction ofthe refrigerant is depicted by the directional arrows.) The super heatedvapor then travels via hot line 104 to heat exchanger 108. Cool waterflowing through heat exchanger 108 (pumped from water heater tank 181 bywater pump 106) cools the fluid down somewhat while heating the water ina heat exchange. The somewhat heated fluid then travels once again to3-way valve/heat pump 105 and is routed towards indoor coils 153 whichtransfers thermal energy (including energy from the compression) to theindoor air by fan 157. The refrigerant then travels to two-way expansionvalve 154 where the fluid undergoes an abrupt reduction in pressure,cooling the fluid (now a mixture of liquid, and gas). The cycle thenrepeats itself as the fluid runs through [evaporator] coil 152.

In some embodiments, a heating element may be added to further heat theambient air which is blown into the space (such as in a case when indoorcoils 152 are not hot enough to heat the indoor space).

Yet another configuration is shown in FIG. 4. FIG. 4 illustrates aschematic diagram of a second embodiment of the invention, with the airconditioner in a heating state. In the depicted embodiment, a connectingpipe 184 and valve 186 are the only components different from the firstembodiment of the invention as depicted in FIG. 2. Connecting pipe 184forms a bridge between intake pipe 172 and cold outlet pipe 174. Valve186 has an open state in which supply water runs from intake pipe 172through connecting pipe 184 into cold outlet pipe 174. Valve 186 has asecond state in which the valve is closed, preventing water from runninginto cold outlet pipe 174.

In the immediate configuration, in a case where hot water is beingutilized during the heating process, cold intake water is diverted fromgoing directly into heating tank 181 (otherwise the cold intake waterwould cool the water in the tank) and goes, rather, directly into heatexchanger 108. Here, the cold intake water from the supply line servesto better cool the refrigerant running through the heat exchanger andcools the water in the heating tank to a lesser degree because the waterenters the tank already slightly warmed from the heat exchanger.Overall, less energy is expended in cooling the refrigerant (fan 155 isactivated less) and heating the water in the heating tank (as the hotwater in the tank will not cool as fast as normally occurs when coldintake water flows directly into the tank). The aforementionedconfiguration is equally effective (if not more so) when air conditioner150 is in a cooling state.

When water pump 106 is active then valve 186 is opened and when thewater pump is deactivated then the valve is closed. Valve 186 may be asolenoid valve.

Heat exchanger 108 may be a coaxial coil heat exchanger (as hinted atearlier). A coaxial heat exchanger, as most basically explained, caninclude a length of tubing having inner lumen disposed with the tubing.In the invention, refrigerant flows through the inner lumen while coolwater flow through the area between the external tubing and the innerlumen. Heat from the inner lumen warms the water while cooling therefrigerant. A counter-flow heat exchanger is envisioned as being thebest mode of practice for the current invention, but the scope of theinvention is in no way limited to either coaxial heat exchangers inparticular or counter-flow heat exchangers in general.

Method of Installation

The method of installation of retrofit unit 100 of the immediateinvention will be better understood with reference to FIG. 5 and atleast FIG. 3. FIG. 5 is a prior art schematic illustration of a waterheating system and an air conditioner prior to installation of theretrofit unit of the invention. Reference is made to both FIGS. 3 and 5,at least.

Step 1—Position housing 101 of retrofit unit 100 including the heatexchanger 108 and water pump 106 between the water heater tank 181 andthe condenser unit of the air conditioner. These two units (tank andcondenser) are often proximally located outside the housing unit (on theroof, attached to an outside wall etc.).

Step 2—Vacuum out refrigerant using a gas recycling machine.

Step 3—Cut refrigerant line 103 between compressor 151 and 3-way valve105. Connect an outlet line 103 from compressor 151 to refrigerant inletport 120 (which is connected to a refrigerant entry on heat exchanger108) and connect an intake line 109 from refrigerant outlet port 122 to3-way valve 105.

Step 4—Replace refrigerant.

Step 5—Empty water heater tank.

Step 6—Connect cold outlet pipe 174 from water tank 181 to the waterinlet port 124 (which is connected to water pump 106). If an outlet pipealready exists (e.g. connecting to a solar panel) then attach a teeconnector (T-connector) with one pipe leading to the existing solarpanel (or other arrangement) and the second pipe to water inlet port124.

Pipe 175 runs from water pump 106 to the water entryway of heatexchanger 108.

Step 7—Connect a (warm) water intake pipe 176 from water outlet port 126back into water tank 181.

Step 8—Refill water tank.

In some embodiments, the unit 100 includes a pressostat 160 which isdisposed in housing 101 and connected to the condensing unit.

Step 9—Connect pressostat 160 to line 152 and to cooling fan 155 of theoutdoor unit.

The pressostat functions to disconnect the cooling fan 155 when pressurein the coils is below a predetermined working/compression pressure. Theprecise working pressure depends primarily on the type of refrigerantused. For example, Freon 22 has a working pressure of approximately 250psi. On the other hand newer Freon 410 has a working pressure of betweenapproximately 450 and 500 psi. The aforementioned examples are merelyexemplary and in no way intended to be limiting. In any case, when thepressure is below the predefined level, then the refrigerant is coolenough and need not be cooled further by cooling fan 155. Therefore,pressostat 160 disconnects the fan, which further saves energy. Whenusing the innovative unit 100 to warm water in cold weather when theheating function of the air conditioner is being used it is necessary todisconnect the pressostat as the external unit now functions as anEvaporator. A circumvention arrangement can be installed to circumventpressostat 160, where the circumvention unit can be activated manuallywith a switch or automatically when the air conditioning unit is turnedto heating.

When heating, the indoor fan 157 is only activated once the coils arehot enough. When unit 100 is activated (i.e. water pump is active) coils153 will take longer to heat up as the heat is first transferred to thewater in the heat exchange. Only once the water in water tank 181 issufficiently hot, and the pump 106 is deactivated, will the pressure beable to build and the coils get hot enough to heat the indoor space. Atthis time indoor fan 157 will activate to blow hot air into the indoorspace. It is therefore generally advisable to activate the airconditioner/heater 150 a sufficient amount of time before heating isrequired within the indoor space.

For example, in winter a family wishes to have hot water available forbathing/showering in the evening (e.g. 6:30 pm) and at the same timeintends to start heating the house. The air conditioner can be activatedat about 6 pm giving the unit about 30 minutes to heat the water in thewater tank (this amount of time is purely arbitrary as the actual timewill depend and many factor including water temperature, strength of airconditioning/heating unit, size of water take, volume and power of waterpump and more). Once the water in water tank 181 has reached asufficient heat (e.g. 45° C.—which is generally sufficient for bathing,washing dishes or running a washing machine) as preset on thermostat179, water pump 106 is deactivated and the refrigerant runs into indoorcoils 153 without being cooled in heat exchanger 108. A sensor (notshown) connected to fan 157 senses that the heat in the coils issufficient and activates indoor fan 157 to blow hot air into the indoorspace (the heat sensor function is preexisting in heating units and notunique to the present innovation). Should the family desire to have theheater work immediately, a switch 112 on a control box 110 of unit 100allows for the manual disconnection of water pump 106 even if the waterin water tank 181 has not reached the desired temperature.

In each of the abovementioned embodiments, the heating unit 100 comes toaugment the function of the heating element in heating tank 181 so thatat any time the heating element can be activated in place of, or incollaboration with, heating unit 100.

For ease of use, control panel 110 can include the aforementionedspecial switches and function buttons including but not limited to:

a switch 114 for circumventing pressostat 160 during the winter months;

a switch 112 for manually deactivating water pump 106;

controlling logic and function buttons 116, for setting a desiredtemperature for thermostat 179 and deferential between the hightemperature above which point water pump 106 is deactivated and lowtemperature below which the water pump is activated;

a display 118, for showing temperature as measured by thermometer 180(heat of water in water tank 181) which can be very useful for knowingwhat the current temperature in water tank 181 is and whether it isnecessary to activate heating unit 100 and/or the heating element of thewater tank.

While the invention has been described with respect to a limited numberof embodiments, it will be appreciated that many variations,modifications and other applications of the invention may be made.Therefore, the claimed invention as recited in the claims that follow isnot limited to the embodiments described herein.

What is claimed is:
 1. A retrofit heat transfer unit, comprising: (a) ahousing for the retrofit unit, including: a water inlet port, a wateroutlet port, a refrigerant inlet port and a refrigerant outlet port; (b)a water pump, in fluid communication with said water inlet port, saidwater pump adapted to pump water from a water source; (c) a heatexchanger, in fluid communication with said water pump, said wateroutlet port, said refrigerant inlet port and said refrigerant outletport; and (d) a thermostat, configured to measure a temperature of saidpumped water, pumped from said water source, such that said water pumpis configured to pump water from said water source when said pumpedwater is below a predefined low temperature and cease to pump said waterwhen said pumped water is above a predefined high temperature, andwherein the retrofit unit is adapted to receive heated refrigerant fluidfrom an air conditioner at said refrigerant inlet port and direct saidreceived heated refrigerant fluid through said heat exchanger andfurther adapted to direct said pumped water into said heat exchangersuch that heat from said heated refrigerant fluid is transferred to saidwater, pumped into said heat exchanger, cooling said heated refrigerantfluid and heating said water, said heated water exiting said housing viasaid water outlet port.
 2. The heat transfer unit of claim 1, whereinsaid heat exchanger is a co-axial coil heat exchanger.
 3. The heattransfer unit of claim 1, wherein said heat exchanger is a plate heatexchanger.
 4. The heat transfer unit of claim 1, wherein said watersource is a domestic water heater.
 5. The heat transfer unit of claim 1,wherein said air conditioner has a cooling function and a heatingfunction for electively cooling and heating an indoor space.
 6. The heattransfer unit of claim 5, wherein the retrofit unit is configured toreceive said heated refrigerant via said refrigerant inlet port fromsaid air conditioner when said air conditioner is in a cooling state. 7.The heat transfer unit of claim 5, wherein the retrofit unit isconfigured to receive said heated refrigerant via said refrigerant inletport from said air conditioner when said air conditioner is in a heatingstate.
 8. The heat transfer unit of claim 1, wherein a differentialbetween said predefined low temperature and said predefined hightemperature is in a range between about 5° C. and 20° C.
 9. The heattransfer unit of claim 1, wherein said water source is a water supplyline from an outdoor water provider and wherein the unit furthercomprises: (e) a valve configured to admit water from said supply linewhen heated water is being drawn from a water heater to a domestic waterdistribution system, wherein said water heater is operationally coupledto the retrofit unit via said water inlet port and said water outletport.
 10. The heat transfer unit of claim 1, further comprising a switchfor electively activating and deactivating said thermostat.
 11. The heattransfer unit of claim 1, further comprising: (e) a pressostat,configured to deactivate an outdoor cooling fan of said air conditionerwhen pressure in outdoor coils of said air conditioner is below apredefined compression pressure.
 12. The heat transfer unit of claim 11,further comprising a means for circumventing said pressostat.
 13. Amethod of increasing the combined efficiency of an air conditioner and awater heater tank, comprising the steps of: (a) interposing a retrofitheat exchange unit between an outdoor unit of the air conditioner andthe water heater tank; (b) cutting a refrigerant line between acompressor and a 3-way valve of the air conditioner; (c) coupling saidrefrigerant line from said compressor to a refrigerant inlet portlocated on a housing of said retrofit unit; (d) coupling saidrefrigerant line said 3-way valve to a refrigerant outlet port locatedon said housing; (e) coupling the water heater tank to a water inletport located on said housing, such that a water pump, disposed insidesaid housing and coupled to said water inlet port, when activated, isconfigured to draw water from the water heater tank; and (f) couplingthe water heater tank to a water outlet port located on said housing,such that heated water, when exiting a heat exchanger disposed in saidhousing and operationally coupled to said water outlet port, exits saidwater outlet port and enters the water heating tank, so that refrigerantfrom the air conditioner heats said water from said water heater tank,in said heat exchanger.
 14. The method of claim 13, further comprisingthe step of: (g) connecting a pressostat, disposed in said housing, tothe air conditioner, for disconnecting a cooling fan of said outdoorunit when pressure in coils of said outdoor unit falls below apredetermined compression pressure.
 15. The method of claim 14, furthercomprising the step of: (h) installing in a control panel, operationallyassociated with said housing of said retrofit unit, a circumventionmechanism for circumventing said pressostat.
 16. The method of claim 13,further comprising the step of: (g) installing in a control paneloperationally associated with said housing, a switch, for electivelyactivating and deactivating said water pump.